Keyboard assemblies of various types are well known including those which employ key operated switches utilizing domes in association with contacts on a printed circuit board such as illustrated in U.S. Pat. No. 3,967,084. It has also been known to provide force transmission systems to operate dome switches which utilize helical spring members between the keycap or push button and the dome, such as illustrated in U.S. Pat. No. 4,156,802. It has also been known to provide keyboard assemblies with dome switches which are constructed to prevent air from being trapped at the underside of the dome and to inhibit dust contamination of the contacts, such as illustrated in U.S. Pat. No. 3,898,421.
Heretofore known force transmission systems as above referred to have been overly complex in that they have included a large number of parts, and it has been difficult to control the force needed to operate the domes. Also, heretofore known keyboard assemblies which include arrangements where the domes do not trap air at their undersides have been constructed to include a number of elements and/or have otherwise been unsatisfactory. For example, where it is intended to prevent dust contamination in the assembly disclosed in above U.S. Pat. No. 3,898,421, the dust filter has not been altogether satisfactory to properly protect the contact surfaces for the domes. Dust contamination leads to switch malfunction. The arrangement in U.S. Pat. No. 4,033,030 utilizes a layer of foam material for allowing air movement behind the domes, which foam material upon aging can disintegrate and contaminate the contacts.